L5K5W6

In this study, a HPA3NT3-analog (FKKLKKLFKKILKLK-NH2) peptide was designed. In this analog, two Trp residues (positions 12, 14) were replaced with Leu, and Arg and Asn (positions 3, 13) were replaced with Lys to investigate the role of amino acid substitution and increased cationicity on antimicrobial and hemolytic activities. In fungal and Gram-negative bacterial cells, HPA3NT3-analog activity was unchanged or slightly enhanced when compared to the HPA3NT3 peptide. In addition, a twofold decrease in activity against Gram-positive bacteria was observed. The HPA3NT3-analog also induced less hemolysis (4.2%) than the HPA3NT3 peptide (71%) at 200 microM. Circular dichroism (CD) spectra revealed that the HPA3NT3-analog peptide had an unordered structure in buffer and egg yolk L-2-phosphatidyl choline (EYPC), but adapted an alpha-helical conformation in 50% 2,2,2-trifluoroethanol (TFE) and negatively charged egg yolk L-2-phosphatidyl glycerol (EYPG), while the parent peptide showed an ordered structure in the EYPC. Additionally, the HPA3NT3-analog peptide induced the leakage of calcein from egg yolk L-2-phosphatidyl ethanolamine (EYPE)/EYPG (7:3 w/w) large unilamellar vesicles (LUVs); however, the activity was slightly weaker than that of the HPA3NT3 peptide. The molecular dynamics (MD) structures revealed that the amino acid substitutions induced a significant variation in peptide structure. These results suggest that the substitutions of Arg and Asn with Lys and two Trp with Leu resulted in small changes in HPA3NT3-analog activity and significant decreases in hemolytic activity.

As potential therapeutic agents, antimicrobial peptides with shorter length and simpler amino acid composition can be better candidates for clinical and commercial development. Here, we attempted de novo design of short (5- to 11-residue) antimicrobial peptides with three kinds of amino acids. Amphipathic helical properties were conferred by using leucines and lysines and two tryptophan residues were positioned at the critical amphipathic interface between the hydrophilic ending side and the hydrophobic starting side. According to this specified rule, 12 model peptides were generated and their helical propensity was confirmed by circular dichroism spectroscopy. Antimicrobial and hemolytic activities were compared with those of the known 12-residue peptide agent, omiganan, which is currently under therapeutic and commercial development. Antimicrobial activities against Gram-negative and Gram-positive bacteria, including a multi-drug resistant strain, were observed for certain 7- to 11-residue models. Among them, the most potent activity was found for a 9-residue peptide (L₅K₂W₂), although it also had severe hemolytic activity. Alternatively, an 11-residue peptide (L₄K₅W₂) with little hemolytic activity was potentially the most useful agent, as it showed higher antibacterial activity than omiganan. These results not only suggest useful candidates for novel antibiotic development, but also provide an efficient strategy to design such peptides.

Extensive use of classical antibiotics has led to the growing emergence of many resistant strains of pathogenic bacteria. Evidence has suggested that cationic antimicrobial peptides (AMPs) are of greatest potential to represent a new class of antibiotics. The largest group of AMPs comprises peptides that fold into an amphipathic alpha-helical conformation when interacting with the target microorganism. In the current study, a series of cationic AMPs of 20 amino acids was designed and synthesised based on four structural parameters, including charge, polar angle, hydrophobicity and hydrophobic moment. The effect of these parameters on antimicrobial activity and selectivity was assessed by structural and biological analyses. Our results indicated that high hydrophobicity and amphipathicity (hydrophobic moment) were correlated with increased haemolytic activity, whilst antimicrobial activity was found to be less dependent on these factors. Three of the synthetic AMPs (GW-Q4, GW-Q6 and GW-H1) showed higher antimicrobial activity and selectivity against a broad spectrum of Gram-positive and Gram-negative bacteria compared with the naturally occurring AMPs magainin 2a and pleurocidin. This study also demonstrates that these rationally designed cationic and amphipathic helical AMPs exhibited high selectivity against several Vibrio spp. and are potential agents for future use in the treatment of these marine pathogens.